1. Field of the Invention
This application relates to energy savings in computer displays and particularly to energy savings in displays of mobile computing systems.
2. Background Art
Mobile computing systems require batteries as an energy source. Mobile computing devices that are not powered by solar cells or self-winding mechanical devices, are powered by rechargeable or non-rechargeable batteries. In meeting the energy needs of mobile computing systems the challenge is to extend battery life beyond a minimal acceptable duration. Ways to increase battery life include increasing the capacity of batteries. Battery life is approximated to the relationship between battery capacity and the average power consumed. Typically, however, increased capacity translates to larger, heavier and more costly batteries. Moreover, rechargeable batteries hold less energy than non-rechargeable batteries. By comparison to battery-powered devices, computer systems such as desktop computers, servers and the like that are powered by electric-outlet-fed power-supplies the energy consumption management has to do with conserving electricity. Thus, whichever power source is used, the design of computing systems must still be biased toward energy conservation.
Energy wise, display subsystems are among the largest consumers of any computing system components. A display subsystem is broadly defined as any combination of the hardware and software modules associated with the visual representation of data in any computing system, and is hereafter referred to simply as xe2x80x9cdisplayxe2x80x9d. In particular, each display subsystem includes a display panel (or cathode ray tubexe2x80x94CRT) and in addition it includes a display controller and display drivers corresponding to the display panel technology and an image processing system module. The image processing module provides geometry and raster processing. A raster image processor (RIP) is a hardware or combination hardware/software module that converts images described in the form of vector graphics statements into raster graphics images or bitmaps. These modules employ computations to generate each screen. A xe2x80x9cscreenxe2x80x9d is the visual presentation (visible image) provided by a display. A system may have one or more displays and each display will have a screen with one or more windows.
Under normal display usage patterns, battery life in battery-powered devices can be extended with advances in battery technology and low-power circuit designs, including energy efficient displays. However, without more, such advances may not meet the energy needs of future mobile computing systems with power metrics dominated by normal display usage patterns.
Thus, designs for energy conservation have turned their focus to the patterns of display usage. As an example, devices have been designed with a number of power metrics to decrease the power usage, including power metrics defined by the power consumed in active mode, idle mode, sleep (inactive) mode, and the like. Changing the display usage pattern by minimizing the display usage and, in turn, energy usage, in the idle and sleep modes, can reduce the average power consumption of the display.
Another example involves reducing the number of pixels to consume less energy. Fonts, icons and graphics can be designed to minimize the number of pixels. With reduced font size the number of pixels to be turned on can be smaller. However, this approach can impact readability.
To further conserve energy, some approaches suggested the possibility of zoned backlighting. However, it was believed that design or manufacturing limitations might preclude mass-production of displays that support zoned backlighting.
It follows that, even with the foregoing approaches, further improvements directed toward achieving energy conservation are desired. The present invention addresses these and related issues.
The present invention provides a method and system for energy-aware software control of the display in order to reduce its overall power consumption. In essence, portions of the display are individually controlled by controlling their corresponding display parameters, such as brightness, color, gray-scale, refresh-rate, etc. The energy saving benefit is derived from adjusting the levels of such display parameters in a controlled manner by the energy-aware software.
The energy-aware software control of individual portions of the display can be used in several different ways. For example, screen area that is of higher importance to the user may be highlighted (e.g., brightly lit and as a result consuming higher power) while the areas of the screen that the user is not concerned about can be turned off, dimly illuminated or modified in some way to consume lower power. Alternatively, the energy-aware software control can choose to selectively turn on color or higher level of gray-scale differentiation only in areas of the screen to be highlighted or in any portions of these screen areas to be highlighted. Indeed, any properly selected part of the screen can be independently controlled to save energy by the energy-aware software control. Whichever way it is implemented, this approach will reduce the average power consumption of the display. Moreover, energy savings of the entire system will depend on the portion(s) of the screen relative to its entire area that are used in typical workloads and the contribution of the display to the total power consumption of the computing system.
As will be explained in more detail below, the present invention involves several aspects. Preferably, these features include means for enabling energy-aware control of individual portions of the screen, a model profiling screen usage patterns by typical applications and their impact on the energy consumption, means to determine when to prompt the energy-aware software control of the display, and means to determine where and how to apply the energy-aware software control.
To operate, the present invention requires the energy-aware software and hardware, i.e., a display, that enables the energy-aware software control of the display at a fine-grained level of granularity. The display hardware is required to support energy-aware control of portions of the display. Examples of display technologies include OLEDs (organic light emitting diodes), tiled displays or a multi-modal hierarchy of displays. OLEDs allow pixels to be individually controlled, while tiled display allow control over groups of pixels. The energy-aware software control exploits the hardware capability for individual control of portions of the display. This software includes a mechanism to determine the screen area of focus in which the user is interested. This mechanism is likely to vary with the various software programs. In a windows-based environment, the area of interest can be directly correlated to the window of focus or any other system parameter. Other applications may require user-initiated intervention in the form of cursor placement to identify the area of interest. Additionally, the software further includes a mechanism to determine the nature of control. For example, with OLEDs, this may include determining if pixels are turned on or off, and if a pixel is turned on, controlling its intensity. In some cases, the software may decide to vary parameters such as the color or refresh rate to control the power.
Advantages of the invention will be understood by those skilled in the art, in part, from the description that follows. Advantages of the invention will be realized and attained from practice of the invention disclosed herein.